This discussion is going beyond the principles of protocol design.
It doesn't matter what organization or document structuring is used
within the server. What matters is how the server presents a model
of its resources (as a namespace) to the client for manipulation.
If the server does not provide a hierarchical namespace, then the
client cannot manipulate it hierarchically.
Document management systems do not use docment ids as their namespace.
They use those things for mapping other namespaces to data in the
management system. This is the same thing that the Unix file system
does with inodes. I am aware that some DMS allow direct access to
their docids using query URLs, but that is a stupid way to present
documents to a user under non-maintenance circumstances. What DMS use
as their namespace is a huge mapping of aliases to doc-ids, and there
is no reason why those aliases can't be hierarchical. They don't
need to be hierarchical all the time, only when the user is performing
a hierarchical operation upon them, and there is no need for upper
layers of the hierarchy to exist outside the alias table.
BTW, these things that I call aliases are just another example of
a direct reference.
The problem with WebDAV is that it uses the generic term collection,
but then restricts collection operations to namespace operations as
if the two were the same thing. Obviously, a collection in a DMS or
a versioning system or even a hypermedia system is just a term for a
named directed graph. So the question you should be asking is whether
WebDAV is making requirements on your use of collection, or just making
requirements on your use of namespace hierarchy for WebDAV operations.
....Roy